Shareholders' Equity (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Amount [Abstract]
Restricted stock grants			$ 921	$ 1,343
Repurchase of common shares			(1,880)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			404,345	394,498
Net income	$ 7,434	$ 4,001	1,847	24,082
Other comprehensive income (loss)	2,679	2,591	11,947	(1,116)
Cash dividends paid to shareholders			(12,250)	(11,885)
Restricted stock grants			921	1,343
Repurchase of common shares			(1,880)
Ending balance	404,930	$ 406,922	404,930	$ 406,922
Additional Paid-in Capital [Member]
Amount [Abstract]
Balance, Beginning period			54,286
Restricted stock grants			919
Repurchase of common shares			(360)
Balance, Period end	$ 54,845		54,845
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted stock grants			919
Repurchase of common shares			$ (360)
Class A [Member]
Shares [Abstract]
Balance, Beginning period (in shares)			2,623,109
Restricted stock grants (in shares)			0
Repurchase of common shares (in shares)			0
Balance, Period end (in shares)	2,623,109		2,623,109
Amount [Abstract]
Balance, Beginning period			$ 112
Restricted stock grants			0
Repurchase of common shares			0
Balance, Period end	$ 112		112
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted stock grants			0
Repurchase of common shares			$ 0
Class B [Member]
Shares [Abstract]
Balance, Beginning period (in shares)			12,460,900
Restricted stock grants (in shares)			37,858
Repurchase of common shares (in shares)			(84,960)
Balance, Period end (in shares)	12,413,798		12,413,798
Amount [Abstract]
Balance, Beginning period			$ 532
Restricted stock grants			2
Repurchase of common shares			(4)
Balance, Period end	$ 530		530
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted stock grants			2
Repurchase of common shares			$ (4)